The invention relates to a hollow platen for printing devices in typewriters and booking machines, filled with sound-absorbing material.
The impact of the types of the printing device, such as type levers, type wheels or type parts, such as the printing needles in the case of screen printing, causes high-frequency vibrations in the platen, which is usually made of a very hard material. These vibrations create an extremely annoying noise which may eventually be health-hazardous, particularly when a number of printing devices are simultaneously in operation. Generally noise levels of from 70 dB to 80 dB are produced by such printing devices.
Because the impact of the type levers on the platen, being, for example, 15 kg force in the case of type levers and slightly less in the case of needle printing devices, cannot be substantially reduced, noise reduction can be realized substantially only by modifying the platen. To this end, it has already been proposed to secure the platen elastically or to provide it with a rubber jacket. However, a platen having a soft impact surface cannot be used, particularly in the case of needle printers, because the printing needles are liable to puncture and thus damage the record carrier.
It has also been attempted to reduce the impact noise by constructing the platen as a hollow body filled with a comparatively soft material. In known arrangements rubber, asbestos fibres, soft metals such as brass or aluminum, vulcanite, wood or resin were used as such a soft material. Either the complete platen consisted of the relevant material, or within a cylinder separate cylinders of the corresponding material were radially or axially arranged. It was found, however, that all these materials did not contribute to an effective noise reduction. Even a solid platen did not produce the desired effect.